Twenty Thirteen: fix comment form layout for inline replies in wide viewports. Fixes #23524, props SriniG and obenland.

(Also fix an extra space that crept into r23461, see #23511.)


git-svn-id: http://core.svn.wordpress.org/trunk@23462 1a063a9b-81f0-0310-95a4-ce76da25c4cd